Modulation effects of hexamethylene bisacetamide on growth and differentiation of cultured human malignant glioma cells

Glycolysis‑related lncRNA may be associated with prognosis and immune activity in grade II‑III glioma

Glucose metabolism, as a novel theory to explain tumor cell behavior, has been intensively studied in various tumors. The present study explored the long non-coding RNAs (lncRNAs) related to glycolysis in grade II-III glioma, aiming to provide a promising target for further research. Pearson correlation analysis was used to identify glycolysis-related lncRNAs. Univariate/multivariate Cox regression analysis and the Least Absolute Shrinkage and Selection Operator algorithm were applied to identify glycolysis-related lncRNAs to construct a prognosis prediction model. Subsequently, multi-dimensional evaluations were used to verify whether the risk model could predict the prognosis and survival rate of patients with grade II-III glioma. Finally, it was verified by functional experiments. The present study finally identified seven glycolysis-related lncRNAs (CRNDE, AC022034.1, RHOQ-AS1, AL159169.2, AL133215.2, AC007098.1 and LINC02587) to construct a prognosis prediction model. The present study further investigated the underlying immune microenvironment, somatic landscape and functional enrichment pathways. Additionally, individualized immunotherapeutic strategies and candidate compounds were identified to guide clinical treatment. The experimental results demonstrated that CRNDE could increase the proliferation of SHG-44 cells. In conclusion, a large sample of human grade II-III glioma in The Cancer Genome Atlas database was used to construct a risk model using glycolysis-related lncRNAs to predict the prognosis of patients with grade II-III glioma.

BET bromodomain inhibitor HMBA synergizes with MEK inhibition in treatment of malignant glioma

(1) Background: BET bromodomain proteins regulate transcription by binding acetylated histones and attracting key factors for, e.g., transcriptional elongation. BET inhibitors have been developed to block pathogenic processes such as cancer and inflammation. Despite having potent biological activities, BET inhibitors have still not made a breakthrough in clinical use for treating cancer. Multiple resistance mechanisms have been proposed but thus far no attempts to block this in glioma has been made. (2) Methods: Here, we have conducted a pharmacological synergy screen in glioma cells to search for possible combination treatments augmenting the apoptotic response to BET inhibitors. We first used HMBA, a compound that was developed as a differentiation therapy four decades ago but more recently was shown to primarily inhibit BET bromodomain proteins. Data was also generated using other BET inhibitors. (3) Results: In the synergy screen, we discovered that several MEK inhibitors can enhance apoptosis in response to HMBA in rat and human glioma cells in vitro as well as in vivo xenografts. The combination is not unique to HMBA but also other BET inhibitors such as JQ1 and I-BET-762 can synergize with MEK inhibitors. (4) Conclusions: Our findings validate a combination therapy previously demonstrated to exhibit anti-cancer activities in multiple other tumour types but which appears to have been lost in translation to the clinic.

HMBA Enhances Prostratin-Induced Activation of Latent HIV-1 via Suppressing the Expression of Negative Feedback Regulator A20/TNFAIP3 in NF-κB Signaling

In the past decade, much emphasis has been put on the transcriptional activation of HIV-1, which is proposed as a promised strategy for eradicating latent HIV-1 provirus. Two drugs, prostratin and hexamethylene bisacetamide (HMBA), have shown potent effects as inducers for releasing HIV-1 latency when used alone or in combination, although their cellular target(s) are currently not well understood, especially under drug combination. Here, we have shown that HMBA and prostratin synergistically release HIV-1 latency via different mechanisms. While prostratin strongly stimulates HMBA-induced HIV-1 transcription via improved P-TEFb activation, HMBA is capable of boosting NF-κB-dependent transcription initiation by suppressing prostratin-induced expression of the deubiquitinase A20, a negative feedback regulator in the NF-κB signaling pathway. In addition, HMBA was able to increase prostratin-induced phosphorylation and degradation of NF-κB inhibitor IκBα, thereby enhancing and prolonging prostratin-induced nuclear translocation of NF-κB, a prerequisite for stimulation of transcription initiation. Thus, by blocking the negative feedback circuit, HMBA functions as a signaling enhancer of the NF-κB signaling pathway.

Identification and characterization of human MIBP1 gene in glioma cell differentiation

Malignant gliomas are the most common and lethal intracranial tumors; differentiation therapy is a promising candidate for their treatment. In order to reveal the mechanisms related to glioma differentiation, after confirming that differentiation was induced by sodium phenylbutyrate in SHG-44 human glioma cells, RNA arbitrary primer differential display was used to screen differentially expressed genes. One gene was found to be upregulated by differential display, and this was also confirmed by reverse northern blot and quantitative real-time PCR analysis. After it was cloned and sequenced, the 505-bp fragment was identified as the MIBP1 (c-myc intron-binding protein 1) gene, also named Hivep2/MBP-2/Schnurri-2. Quantitative real-time PCR analysis of 30 human tissue samples revealed that the expression of MIBP1 tended to decrease with increasing WHO grade and was significantly depressed in the high malignancy gliomas group (WHO grade IV). We cloned and sequenced the MIBP1 gene, which was accepted by GenBank as number DQ231041. Finally, transfection of MIBP1 in a reverse transcription vector into glioma cells inhibited cell growth, induced differentiation, and blocked the cell cycle. Here, we identify and describe the structure and function of a differentiation-related gene, human MIBP1, in human glioma.

Cyclic AMP-dependent regulation of differentiation of rat C6 glioma cells by panaxydol

OBJECTIVES

Preliminary works have indicated that panaxydol possesses growth inhibition and induces differentiation in rat C6 glioma cells. However, the molecular mechanism underlying this differentiation remains unknown. We sought to investigate the role of cyclic adenosine monophosphate (cAMP) in cellular differentiation induced by panaxydol.

METHODS

C6 cells were treated with panaxydol and various specific inhibitors, and the inhibition of cell growth was assessed by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and homotransplantation in nude mice. Astrocytic processes were quantified under a phase-contrasted microscope. Glial fibrillary acidic protein expression and cell migration were carried out by Western blot and scratch-wound test, respectively. In addition, the intracellular cAMP concentration was measured by immunoassay.

RESULTS

Panaxydol induces the elevation of intracellular cAMP concentration in C6 cells. The effects of growth inhibition in vitro and in vivo and induction of differentiation in C6 cells by panaxydol could be inhibited by the cAMP inhibitor, Rp-adenosine 3',5'-cyclic monophosphothioate, but not by protein kinase A or protein kinase C specific inhibitors.

CONCLUSION

These results suggest that the cAMP-dependent pathway may regulate cellular proliferation, migration and differentiation in C6 glioma cells by panaxydol.

Overexpression of CDC2/CyclinB1 in gliomas, and CDC2 depletion inhibits proliferation of human glioma cells in vitro and in vivo

Background

Gliomas are the most common and aggressive primary brain tumors for which unfortunately no effective treatment modalities exist despite advances in molecular biology as the knowledge base to unravel the extremely complex molecular mechanisms of tumorigenesis is limited. In this study an attempt has been made to understand the molecular pathological basis of tumorigenesis which led to an identification of an oncogene, CDC2, and an epigenetic strategy has been evaluated to control the tumorigensis by downregulating this oncogene.

Methods

Tissue microarrays were utilized to investigate the expression of genes in a large number of tumor samples and to identify overexpressed genes which could be potentially causing tumorigenesis. Retroviral vectors expressing short hairpin RNAs (shRNAs) targeted against CDC2 were designed and transducted into human glioma cell line ex vivo in order to downregulate the expression of CDC2. Real-Time PCR was used to determine the level of CDC2 mRNA. Western Blotting was used to determine the level of expression of CDC2 protein as measure to quantify down regulation of CDC2 expression along with use of flow cytometry to investigate effect of shRNAs on cell cycles and detection of apoptosis. Following ex vivo study, viral particles containing small interfering RNA for CDC2 were subsequently injected into xenogeneic graft tumor of nude mice and the weight of human glioma xenografts, survival and resulting phenotypic changes of target gene were investigated.

Results

Human glioma tissue microarrays indicated the positive expression rates of CDC2/CyclinB1 with a positive correlation with pathologic grades (r = 0.982, r = 0.959, respectively). Retroviral vectors expressing short hairpin RNAs (shRNAs) against CDC2 caused efficient deletion of CDC2, cellular G2/M arrest concluding in apoptosis and inhibition of proliferation in human glioma cells U251 and SHG-44 cell lines ex vivo. And the viral particles containing small interfering RNA for CDC2 were subsequently injected into subcutaneous and intracranial xenogeneic graft tuomrs of nude mice. For subcutaneous tumors, injection of CDC2-shRNA retroviruses significantly decreased tumor weight and volume compared with control. Immunohistochemistry indicated that CDC2 are negative and TUNEL are positive in tumors treated with recombinant retrovirus. For mice implanted with intracranial gliomas, treatment of CDC2-shRNA retroviruses increased survival times compared with control.

Conclusion

CDC2 gene plays an important role in the proliferation of human gliomas. Downregulation of CDC2 could potentialy inhibit human gliomas cells growth ex vivo and in vivo. From these results, it was suggested that CDC2 might be a potential target on gene therapy of human gliomas.

Differentiation profile of brain tumor stem cells: a comparative study with neural stem cells

Understanding of the differentiation profile of brain tumor stem cells (BTSCs), the key ones among tumor cell population, through comparison with neural stem cells (NSCs) would lend insight into the origin of glioma and ultimately yield new approaches to fight this intractable disease. Here, we cultured and purified BTSCs from surgical glioma specimens and NSCs from human fetal brain tissue, and further analyzed their cellular biological behaviors, especially their differentiation property. As expected, NSCs differentiated into mature neural phenotypes. In the same differentiation condition, however, BTSCs exhibited distinguished differences. Morphologically, cells grew flattened and attached for the first week, but gradually aggregated and reformed floating tumor sphere thereafter. During the corresponding period, the expression rate of undifferentiated cell marker CD133 and nestin in BTSCs kept decreasing, but 1 week later, they regained ascending tendency. Interestingly, the differentiated cell markers GFAP and beta-tubulinIII showed an expression change inverse to that of undifferentiated cell markers. Taken together, BTSCs were revealed to possess a capacity to resist differentiation, which actually represents the malignant behaviors of glioma.

Phenylbutyrate and phenylacetate induce differentiation and inhibit proliferation of human medulloblastoma cells

PURPOSE

Phenylbutyrate (PB) and phenylacetate (PA) have antiproliferative and differentiation-inducing effects in malignant tumors, and had been evaluated in Phase I/II clinical trials. This study was undertaken to evaluate their antitumor activities in medulloblastomas.

EXPERIMENTAL DESIGN

The biological effects of PB and PA, ranging from 0.1 mM to 3 mM, on two medulloblastoma cell lines (DAOY and D283-MED) were examined using various long-term in vitro and in vivo assays for morphology, proliferation, differentiation, anchorage-independent growth, apoptosis, and tumorigenicity.

RESULTS

PB and PA can both induce morphological changes and suppress proliferation in a time- and dose-dependent manner. These effects were more pronounced with PB and became irreversible in D283-MED cells after continuous exposure to 3 mM PB for 28 days. Both PB and PA were able to increase expression of glial marker glial fibriliary acidic protein and neuronal marker synaptophysin in two cell lines. For anchorage-independent growth, PB showed a more significant suppression than PA in D283-MED cells. PB caused more pronounced cell cycle arrest and remarkably reduced tumorigenicity in D283-MED cells than in DAOY cells. Apoptosis was readily induced in D283-MED cells with either low dose of PB or short-term treatment. In contrast, much higher concentrations of PB or longer treatment were required to achieve similar effect with DAOY cells. PB induced increased histones H3 acetylation in both cell lines, but histone H4 acetylation was only observed in D283-MED cells.

CONCLUSIONS

PB, through induction of hyperacetylation of histone H3 and H4, is a much more potent antitumor agent than PA. 283-MED cells are more responsive to PB than DAOY cells, which may be dependent on their original state of differentiation as well as the changes of histone H4 acetylation status.

Growth arrest and apoptosis of human hepatocellular carcinoma cells induced by hexamethylene bisacetamide

AIM: To investigate the cellular effects of hybrid polar compound hexamethylene bisacetamide (HMBA) on the growth and apoptosis of human hepatocellular carcinoma cells and to provide the molecular mechanism for potential application of HMBA in the treatment of liver cancer.

METHODS: Effects of HMBA on the growth of human hepatocellular carcinoma SMMC-7721 cells were assayed by MTT chronometry. Apoptosis induced by HMBA was detected by phase-contrast microscopy, flow cytometry, propidium iodide staining and immunocytochemical analysis.

RESULTS: The growth of SMMC-7721 cells was significantly inhibited by HMBA, and the growth inhibitory rate was 51.1%, 62.6%, 68.7% and 73.9% respectively after treatment with 5.0, 7.5, 10.0 and 12.5 mmol/L of HMBA. In the cells treated with 10 mmol/L of HMBA for 72 h, the population of cells at sub-G₁ phase significantly increased, and the apoptotic bodies and condensed nuclei were detected. Moreover, treatment of SMMC-7721 cells with 10 mmol/L of HMBA down-regulated the expression of Bcl-2 anti-apoptotic protein, while slightly up-regulated the level of pro-apoptotic protein Bax.

CONCLUSION: Treatment with 10.0 mmol/L of HMBA can significantly inhibit the growth and induce apoptosis of human hepatocellular carcinoma SMMC-7721 cells by decreasing the ratio of Bcl-2 to Bax.

Induction of differentiation in rat C6 glioma cells with Saikosaponins

The effects of saikosaponins (a, b(1), b(2), c, d), isolated from Bupleurum Radix, on the induction of differentiation in rat C6 glioma cells were studied. Saikosaponins a and d were shown to inhibit cell proliferation and alter cell morphology. In addition to cytostasis, the enzymatic activities of glutamine synthetase (GS) and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) were also noticeably increased after treatment with saikosaponin a. Nevertheless, saikosaponin d only showed an increase of GS activity, no significant changes in CNP activity were found. These results suggest that saikosaponin a can induce the differentiation of C6 glioma cells into astrocytes and/or oligodendrocytes, but saikosaponin d can only induce the differentiation of C6 glioma cells into astrocytes.

Therapeutic effects of sodium butyrate on glioma cells in vitro and in the rat C6 glioma model

OBJECTIVE

Preliminary in vitro studies have indicated that sodium butyrate inhibits the proliferation of cultured glioma cells and induces cellular differentiation, making it potentially useful as a therapeutic agent for patients with glioblastoma multiforme. The purpose of this study was to expand on the preliminary research by investigating the effects of sodium butyrate on multiple cell lines, explanted cells from glioblastoma tumor specimens, and in vivo in the rat C6 glioma brain tumor model.

METHODS

Four malignant glioma cell lines (A-172, T98G, U118MG, and C6) and two primary cell cultures derived from human glioblastoma tumor specimens were treated with 2 mmol/L sodium butyrate for up to 72 hours. Sodium butyrate-induced effects on cell morphology, proliferation, cell cycle distribution, migration, glial fibrillary acidic protein staining, and S100beta protein content were determined. For in vivo studies, a total of 64 male Wistar-Furth rats underwent operations to implant C6 glioma cells stereotactically or were used as controls. The rats were treated with escalating doses of sodium butyrate by microinfusion with Alzet minipumps (Durect Corp., Cupertino, CA).

RESULTS

Sodium butyrate treatment in vitro produced changes in morphology and glial fibrillary acidic protein expression indicative of cellular differentiation. In cell lines and explanted cells, sodium butyrate consistently inhibited glioblastoma cell proliferation (to 51 +/- 6% that of controls) and migration (to 46 +/- 17%). Intratumoral infusion of 40 mmol/L sodium butyrate prolonged the survival of Wistar-Furth rats with intracerebral C6 tumors (P = 0.013) without detectable toxicity.

CONCLUSION

These data support further consideration of direct interstitial infusion of sodium butyrate in a Phase I clinical study for patients with recurrent glioblastoma multiforme.

Multi-agent cytostatic treatment of 'low-grade' gliomas

The rationale and current supporting evidence for a complementary, multi-agent, low-toxicity, chronic, cytostatic therapeutic approach to treating patients with gliomas is presented in detail. This strategy would involve the simultaneous treatment of patients with DNA/chromosomal stabilizing agent(s), anti-angiogenesis agent(s), and anti- invasion agent(s), with or without the addition of a low-toxicity antiproliferation agent. Oral agents would be the ideal for this chronic, potentially life-long, therapeutic approach. The most logical target group would be patients with newly diagnosed "low-grade" gliomas rather than those with more malignant (usually recurrent) gliomas.

Control of proliferation and survival of C6 glioma cells with modification of the nerve growth factor autocrine system

Nerve growth factor (NGF) plays an important physiological role in differentiation and survival of various types of neurons. Glial cells and glial tumor cells synthesize multiple neurotrophic factors including NGF and secrete them into the surrounding environment; however, the mechanisms of NGF and the significance of NGF receptors have not been studied in detail. The C6 glioma cell line can synthesize NGF, respond to exogenous application of NGF and stimulate the expression of NGF receptor in an autocrine manner. In order to determine the significance of such an NGF autocrine system, the effects of exposure to exogenous NGF and deprivation of endogenous NGF were examined in a C6 glioma cell line in vitro. Exogenous NGF significantly inhibited maintenance of the cell number and thymidine incorporation. Morphological changes, including the formation of growth cones, outgrowth of processes and cellular hypertrophy, were observed, concurrently, indicating that exogenous NGF stimulated differentiation and thereby inhibited proliferation of the cells. Deprivation of endogenous NGF with anti-NGF antibody elicited a rapid decrease in cell number and thymidine incorporation, and led almost all of the cells to death within 8 days. The protein synthesis inhibitor, cycloheximide, strongly inhibited the death of NGF-deprived cells, suggesting the involvement of an active process requiring synthesis of suicide proteins. These findings imply that the NGF autocrine system plays a significant role in regulating the differentiation and survival of C6 glioma cells, similarly to neuronal cells.

Inhibitory effects of phenylbutyrate on the proliferation, morphology, migration and invasiveness of malignant glioma cells

The purpose of this study was to characterize the effects of sodium 4-phenylbutyrate (phenylbutyrate) on the proliferation, morphology, migration and invasiveness of malignant glioma cells in vitro. Phenylbutyrate is a novel differentiating and cytotoxic compound used clinically with low toxicity in the treatment of beta-thalassemia, sickle cell anemia and urea cycle disorders. Preliminary clinical trials testing phenylbutyrate as an anti-cancer agent have included patients with malignant glioma. However, little information is available regarding the effects of phenylbutyrate on glioma cells, particularly with respect to the expression of genes important in the pathogenesis of glial malignancy. In experiments reported here, glioma cell lines and explant cells from a tumor patient were exposed to 2, 4 and 8 mM phenylbutyrate and compared to untreated control cells. The effect on cellular proliferation was assessed using cell counts and DNA flow cytometry. Changes in morphology were evaluated using vimentin staining. Scratch and Matrigel assays were performed to assess changes in cellular migration and invasiveness. Finally, Northern blot analysis was used to study c-myc and urokinase expression. Phenylbutyrate was found to have dose-dependent inhibitory effects on glioma cell proliferation, morphology, migration, invasiveness and c-myc and urokinase expression. Mean growth-inhibitory (IC50) phenylbutyrate concentrations ranged from 0.5 mM for T98G cells to 5.0 mM for explant cells. Phenylbutyrate treatment reduced % S phase cells, increased % G0/G1 cells, and produced morphologic changes consistent with induction of differentiation. 24 hours of treatment with 4 mM phenylbutyrate resulted in a 50% reduction in migration and invasiveness. Northern blots showed a decrease in urokinase and c-myc expression at non-cytotoxic doses. We conclude that phenylbutyrate is a promising candidate compound for treating patients with malignant glioma.

Molecular characterization of glioblastoma cell differentiation

OBJECTIVE

Induction of cellular differentiation continues to be an attractive therapeutic strategy for malignant glioma. The purpose of this study was to develop a convenient in vitro model system for glioblastoma differentiation and to then characterize it using conventional techniques and flow cytometry.

METHODS

A subline of U138 MG cells ("U138B") was treated with 0 to 4 mmol/L sodium butyrate (or serum deprivation) for up to 96 hours. Cells were initially studied for effects on proliferation, morphology, and glial fibrillary acidic protein (GFAP) staining. Northern blot and immunoblot analyses of c-myc expression were performed. Multiparameter flow cytometry was then used to analyze GFAP, c-myc protein, and total cellular protein fluorescence and to relate them to changes in cell cycle distribution.

RESULTS

Butyrate treatment produced a dose-dependent inhibition of cellular proliferation and changes in morphology, GFAP staining, and c-myc expression consistent with a differentiation response. Detailed flow cytometric studies, including subpopulation analysis, showed that during 72 hours of treatment with 2 mmol/L butyrate, mean GFAP fluorescence increased to 420%, whereas c-myc protein decreased to 45 +/- 13% and total cellular protein increased to 181 +/- 17%. The effects of butyrate were distinct from those of serum deprivation and were not simply the result of cells shifting into Gzero/G1.

CONCLUSION

The butyrate-induced responses of the U138B cell line provide a convenient model system for studying the molecular events accompanying the differentiation of glioblastoma cells. Multiparameter flow cytometry is a useful technique for characterizing such differentiation.

Growth-inhibitory and differentiation-inducing activity of dimethylformamide in cultured human malignant glioma cells

OBJECTIVE

To determine the growth-inhibitory and differentiation-inducing activity of dimethylformamide (DMF) on a human glioma cell line (SHG-44). DMF is a type of polar solvent and a potent differentiation-inducing agent in many kinds of human solid tumors, yet its effect on human glioma remains unclear.

METHODS

The effects of DMF on cell proliferation using 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, cell cycle distribution (with flow cytometry), colony-forming efficiency in double-layer soft agar, tumorigenicity in athymic nude mice, morphological changes, and glial fibrillary acidic protein expression were studied.

RESULTS

At dose ranges of 0.25, 0.5, 0.75, and 1.0%, DMF caused a dose-dependent proliferation inhibitory effect in monolayers and a marked dose-dependent suppression of colony-forming efficiency in double-layer soft agar with a complete loss of colony-forming ability in cells exposed to 0.75 and 1.0% DMF. Accumulation of cells in G0/G1 phases was observed in DMF-treated (0.5 and 1.0%) cells, also in a dose-dependent manner. SHG-44 cells exposed to DMF (0.5 and 1.0%) for 15 days changed morphologically from small spindle-shaped to large polygonal and flattened stellate cells with multiple slender processes. These cells were still tumorigenic in athymic nude mice, but the growth of xenografts was remarkably reduced, especially in the 1.0% DMF-treated group. The expression of glial fibrillary acidic protein was notably increased by DMF (0.5 and 1.0%). Washout experiments revealed that the effects of DMF on cell proliferation and cell cycle distribution were reversible.

CONCLUSION

Our results suggest that DMF drove the SHG-44 cells to a more mature phenotype with inhibited growth.